Adenosine A1 receptor antagonist prolongs survival in the hypoxic rat

The novel combination of theophylline and bambuterol as a potential treatment of hypoxemia in humans

Hypoxemia can be life-threatening, both acutely and chronically. Because hypoxemia causes vascular dysregulation that further restricts oxygen availability to tissue, it can be pharmacologically addressed. We hypothesized that theophylline can be safely combined with the β2-adrenergic vasodilator bambuterol to improve oxygen availability in hypoxemic patients. Ergogenicity and hemodynamic effects of bambuterol and theophylline were measured in rats under hypobaric and normobaric hypoxia (12% O₂). Feasibility in humans was assessed using randomized, double-blind testing of the influence of combined slow-release theophylline (300 mg) and bambuterol (20 mg) on adverse events (AEs), plasma K⁺, pulse, blood pressure, and drug interaction. Both drugs and their combination significantly improved hypoxic endurance in rats. In humans, common AEs were low K⁺ (<3.5 mmol/L; bambuterol: 12, theophylline: 4, combination: 13 episodes) and tremors (10, 0, 14 episodes). No exacerbation or serious AE occurred when drugs were combined. A drop in plasma K⁺ coincided with peak bambuterol plasma concentrations. Bambuterol increased heart rate by approximately 13 bpm. Drug interaction was present but small. We report promise, feasibility, and relative safety of combined theophylline and bambuterol as a treatment of hypoxemia in humans. Cardiac safety and blood K⁺ will be important safety endpoints when testing these drugs in hypoxemic subjects.

Rolofylline: a selective adenosine 1 receptor antagonist for the treatment of heart failure

BACKGROUND

Co-existent cardiac and renal dysfunction is increasingly recognized as both a predictor and mediator of poor outcomes in patients with advanced heart failure. Novel therapies, including adenosine receptor antagonists, are currently under development for the treatment of 'cardiorenal syndrome'.

OBJECTIVES

To review the pathophysiologic rationale for using rolofylline, a selective adenosine 1 receptor antagonist, in patients with cardiorenal syndrome; and to provide a critical overview of safety and efficacy data from clinical studies.

METHODS

We reviewed published data on the pharmacology of rolofylline, and used this to inform a comprehensive summary of preclinical and clinical trials. Cardiac and renal effects, and safety data with a particular reference to seizures, are highlighted.

RESULTS/CONCLUSION

Rolofylline facilitates diuresis and preserves renal function in patients with acute decompensated heart failure and renal dysfunction. Pilot data also suggest beneficial effects on symptoms and short-term outcomes. The risk of seizures may be minimized by excluding high-risk patients.

Microwave-assisted ring closure reactions: synthesis of 8-substituted xanthine derivatives and related pyrimido- and diazepinopurinediones

BACKGROUND

Poly-substituted xanthine derivatives are an important class of compounds in medicinal chemistry. Substitution at the 8-position of the purine ring is generally accessible by ring closure of a carboxamido-substituted uracil precursor. Although several procedures to accomplish this synthetic step have been suggested, it still remains difficult in many cases.

RESULTS

Ring closure reaction with hexamethyldisilazane was studied under microwave conditions. Reaction times were dramatically reduced by the application of microwaves in the syntheses of the 8-styrylxanthine derivative istradefylline, and in the preparation of 2-substituted pyrimido [1,2,3-cd]purines. Furthermore, the new procedure allowed the preparation of a previously unaccessible diazepino [1,2,3-cd]purine. Yields were generally improved by the new method. The addition of THF as a co-solvent proved to be crucial.

CONCLUSION

A new, fast, and efficient ring closure method for the imidazole ring of xanthine derivatives and related tricyclic compounds has been developed. Apart from improving the syntheses of known compounds, some of which are important pharmacological tools or in development as novel drugs, it allows the preparation of 2-substituted diazepino [1,2,3-cd]purines--a new class of tricyclic purine derivatives.

Adenosine A1 antagonism attenuates beta-adrenergic-resistant sudden hypoxic cardiac insufficiency

OBJECTIVES

In states such as hypoxia, shock, and cardiac arrest, compromised systemic oxygenation or perfusion appears to induce cardiac insufficiency that can be resistant to beta-adrenergic drugs. Elevated levels of adenosine may mediate such beta-adrenergic-resistant cardiac insufficiency via the adenosine A(1) receptor (A(1)AdoR). The objective of this study was to test the hypothesis that selective A(1)AdoR antagonism attenuates hypoxic cardiac insufficiency more efficaciously than beta(1)-adrenergic agonism or nonselective adenosine antagonism.

METHODS

Rats were paralyzed and ventilated to a pCO(2) level of 35-40 mm Hg. Ten minutes before hypoxia (inspired o(2) concentration = 5%), rats were treated intravenously with one of the following: 0.1 mg/kg BG-9719 (n = 9), 10 mg/kg NPC-205 (n = 10; BG-9719 and NPC-205 are selective A(1)AdoR antagonists, with durations of action of 30-60 minutes and 60-90 minutes, respectively), 10 mg/kg aminophylline (n = 12), 5 microg/kg/min dobutamine (n = 11), or control solutions. These drug doses maximized survival duration in dose-response studies.

RESULTS

Before hypoxia, cardiac work was increased more by aminophylline and dobutamine than by BG-9719. Mean (+/-SEM) duration of survival (in minutes) after hypoxia increased from <13 (control solutions) to 13.8 (+/-1.4) (dobutamine), 20.0 (+/-1.6) (aminophylline), 31.7 (+/-4.6) (BG-9719), and 40.5 (+/-7.5) (NPC-205) (p < 0.0001). Heart rate and dP/dt decreased rapidly after hypoxia, but decreases were attenuated with BG-9719 and NPC-205 compared with dobutamine (p < 0.05) and tended toward attenuation with aminophylline.

CONCLUSIONS

BG-9719 and NPC-205 improved survival duration, heart rate, and left ventricular contractility during hypoxia more efficaciously than dobutamine and possibly aminophylline. Selective A(1)AdoR antagonists warrant further study as alternatives to beta-adrenergic agonists in hypoxia, shock, and cardiac arrest, in which compromised systemic perfusion or oxygenation impairs cardiac output.

Comparison of adenosine, isoflurane, and desflurane on myocardial tissue oxygen pressure during coronary artery constriction in dogs

OBJECTIVE

To compare adenosine-, isoflurane-, or desflurane-induced hypotension with and without left anterior descending (LAD) coronary artery constriction for the effects on myocardial tissue oxygen pressure (PmO(2)) in dogs.

DESIGN

Prospective, randomized, nonblinded.

SETTING

University teaching hospital.

PARTICIPANTS

Male nonpurpose-bred dogs (n = 18).

INTERVENTIONS

Dogs were anesthetized with 1.5% isoflurane (n = 12) or 8% desflurane (n = 6). A flow probe and balloon occluder were placed on the LAD artery. A probe that measured myocardial oxygen pressure was inserted into the middle myocardium in the LAD region. Myocardial oxygen consumption (MVO(2)) was calculated as LAD flow x arterial minus coronary sinus oxygen content.

MEASURES AND MAIN RESULTS

Measures were made during hypotension produced by adenosine infusion, 2.8% isoflurane, or 14% desflurane with and without LAD constriction to decrease blood flow 30%. Without LAD artery constriction, adenosine infusion increased LAD flow 90% and MVO(2) 70%, 2.8% isoflurane produced no change in MVO(2), and 14% desflurane decreased MVO(2) 25%, but no treatment changed PmO(2). LAD artery constriction decreased PmO(2) 50% by itself. Adenosine infusion during LAD constriction decreased tissue oxygen pressure an additional 60%, 2.8% isoflurane produced no change, and 14% desflurane increased PmO(2) 100%.

CONCLUSION

There was an inverse relationship between the effect of adenosine, 2.8% isoflurane, and 14% desflurane on MVO(2) and PmO(2) during ischemia. This is consistent with reports that increasing oxygen demand worsens myocardial ischemia.